Composition containing highly unsaturated fatty acid or alkyl ester thereof and a method for producing the same

ABSTRACT

PROBLEM To provide a composition comprising highly enriched PUFA or its alkyl esters while containing fatty acid esters of 3-MCPD at adequately low concentrations and to provide an efficient method for producing the composition. 
     MEANS FOR SOLVING A composition that contains fatty acids or fatty acid alkyl esters as its major component, the composition containing highly unsaturated fatty acid or alkyl ester thereof, wherein the proportion of the highly unsaturated fatty acid in the constituent fatty acids of the composition is 50 area % or more and wherein the concentration of 3-MCPD as found upon analyzing the composition by American Oil Chemists&#39; Society official method Cd 29b-13 assay A is less than 1.80 ppm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.16/404,662, filed May 6, 2019, which claims priority to JP 2018-232498,filed Dec. 12, 2018.

TECHNICAL FIELD

The present invention relates to a composition containing highlyunsaturated fatty acid or alkyl ester thereof, and to a method forproducing the same.

BACKGROUND ART

The compound 3-chloropropane-1,2-diol (3-MCPD) is suspected ofcarcinogenicity and various countries and regions including EU haveregulations on the concentration of 3-MCPD in food products. It is alsoknown that 3-MCPD is produced in fats and oils with diacylglycerol (DAG)or monoacylglycerol (MAG) working as a substrate (Non-Patent Document1). Ever since the reporting of 3-MCPD present in diacylglycerol(DAG)-rich fats and oils, attempts have been made to reduce its contentin the fats and oils by various methods. For example, with 3-MCPD beingknown to form at high temperatures, Patent Documents 1 and 2 disclosethat the concentrations of 3-MCPD forming substances in the fats andoils can be reduced by treatment with an adsorbent, by lowering thedeodorizing temperature, or by shortening the treatment time. However,these methods are specifically intended for reducing the concentrationsof substances that form 3-MCPD in the production of triacylglycerol andPatent Documents 1 and 2 do not describe any method for reducing theconcentrations of fatty acid esters of 3-MCPD in the production of alkylesters.

Polyvalent unsaturated fatty acids (PUFAs) are known to have a varietyof functional properties and highly enriched PUFAs are utilized in foodproducts, supplements, pharmaceuticals or cosmetics. In the process ofenhanced enrichment, whereby the proportion of the desired PUFA(s) isincreased among the fatty acids of a starting composition, PUFAs undergoconversion from triacylglycerol-based glycerides to alkyl esters withlower alcohols. Hence, highly refined and enriched PUFAs which are usedin food products, supplements, pharmaceuticals or cosmetics are in mostcases in the form of alkyl esters. No method has been known to date thatis capable of reducing the concentrations of fatty acid esters of 3-MCPDin those highly enriched alkyl esters of PUFAs.

Factors that are known to affect the formation of fatty acid esters of3-MCPD include a chlorine source, substrates such as MAG and DAG, aswell as the time of treatment at high temperature (Non-Patent Documents1 and 2). However oils that are used as the raw material forPUFA-containing food products and so forth typically contain such smallamounts of chlorine sources and substrates, such as MAG and DAG, forfatty acid esters of 3-MCPD, that their effects on the refining of theend product PUFA are extremely small and the need to remove them is notgenerally recognized. In this connection, complete removal of chlorinesources and substrates such as MAG and DAG is not currently performedfor reasons of the technical difficulties involved and the potentialeffects on productivity such as the percent recovery of PUFAs.

Rectification is a distillation technique that can potentially achievehigh separation performance; on the other hand, it requires an internalpacking and refluxing, which often results in the need for heating attemperatures higher than 150° C. Molecular distillation and short-pathdistillation which involve heating temperatures not higher than 150° C.can be performed at relatively lower temperatures than rectification;however, in order to achieve satisfactory enrichment of PUFA, repeatedprocessing is required and this presents the risk of forming largeamounts of 3-MCPD in the distillation of PUFA.

Urea adduct formation and HPLC are techniques that perform separation inaccordance with the structures (e.g., chain length, the number of doublebonds, and so forth) of fatty acids that constitute the molecule to beseparated; however, if the starting material contains 3-MCPD in the formof di- or mono-fatty acid esters, they are difficult, depending on thetypes of the constituent fatty acids, to separate from the desired alkylesters, with the result that fatty acid alkyl esters with a reducedcontent of fatty acid esters of 3-MCPD are difficult to obtain in aconsistent manner.

Hence, refining steps such as solvent removal and distillation thatinclude a heating procedure obviously involve the risk of forming fattyacid esters of 3-MCPD and even methods such as urea adduct formation andHPLC are not necessarily capable of removing the various fatty acidesters of 3-MCPD that are contained in the starting material.

PRIOR ART LITERATURE Patent Literature

-   Patent Document 1: JP 2011-147435 A-   Patent Document 2: JP 2011-147436 A

Non-Patent Literature

-   Non-Patent Document 1: Eur. J. Lipid Sci. Technol. 114, 1268-1273    (2012)-   Non-Patent Document 2: Eur. J. Lipid Sci. Technol. 115, 735-739    (2013)-   Non-Patent Document 3: J. Agric. Food. Chem. 63(6), 1839-48 (2015)

SUMMARY OF INVENTION Technical Problem

In many cases, PUFA-containing fats and oils also contain 3-MCPD or itsfatty acid esters that derive from the starting material or result fromthe oil pressing (extraction) and refining steps. When the glycerides inthe fats and oils are alkyl esterified, MAG and DAG will remain or theirconcentrations are more likely to increase, creating an environment inwhich fatty acid esters of 3-MCPD are prone to form. Furthermore, therefining of alkyl esters often involves the step of solvent removal aswell as distillation steps such as molecular distillation, short-pathdistillation, and rectification, and fatty acid esters of 3-MCPD canform in each of these steps. In chromatography and urea adductformation, no external temperature is applied, so the possibility forthe formation of fatty acid esters of 3-MCPD is low but, on the otherhand, there is a risk that the concentrations of fatty acid esters of3-MCPD that are already contained cannot be adequately reduced.

An object, therefore, of the present invention is to provide acomposition comprising highly enriched PUFA or alkyl ester thereof whilecontaining fatty acid esters of 3-MCPD at adequately low concentrationsand to provide an efficient method for producing the composition.

Solution to Problem

The present inventors conducted an intensive study with a view toattaining the above-stated objects and have found that C20-C22 fattyacid alkyl ester fractions, which are to be enriched in PUFA, and 3-MCPDmono-fatty acid esters, which have one molecule of C14 or C16 fatty acidbound thereto, show similar behaviors in distillation. The presentinventors further found that by reducing the content of a monoacylglycerol (MAG), especially one having the C14 or C16 fatty acid boundthereto, that is present in the starting material, the concentrations ofthe mono-fatty acid esters of 3-MCPD in the C20-C22 fatty acid alkylester fractions can be reduced.

The present inventors have also found that the rate at which the fattyacid esters of 3-MCPD form varies considerably depending on the changein the concentration of a trace (≤1 ppm) metal such as iron that iscontained in the starting material. It had been reported that the ironcontent would have an effect on the formation of fatty acid esters of3-MCPD from triacyl glycerol (Non-Patent Document 3). However, thedisclosure in Non-Patent Document 3 is about the result of a study onthe formation of fatty acid esters of 3-MCPD in the presence of aconsiderably large amount of Fe²⁺ or Fe³⁺ and it was not known that thetrace iron usually contained in the oil as the raw material for theproduction of PUFA alkyl esters would have an effect on the formation offatty acid esters of 3-MCPD.

The yet-to-be-enriched PUFA alkyl esters as produced from fish oil andother raw materials are generally low in the degree of refinement, sotheir iron concentration can vary depending on the iron content in theoil as the starting material. The iron concentration of theyet-to-be-enriched PUFA alkyl esters can also vary considerablydepending on other factors including the quality of the starting oil tobe extracted, the method of extraction, and the method of refining.Therefore, if the iron concentration is increased, heating treatmentssuch as distillation can lead to an unexpectedly high concentration offatty acid esters of 3-MCPD. We find that such an unexpected rise in theconcentration of fatty acid esters of 3-MCPD can be effectivelysuppressed by ensuring that the concentration of iron before the heattreatment such as distillation is adjusted to less than 0.20 ppm.

The present inventors conducted further studies based on these findingsand have finally accomplished the present invention.

Briefly, the present invention relates to the following:

[1] A composition that contains fatty acids or fatty acid alkyl estersas its major component, the composition containing highly unsaturatedfatty acid or alkyl ester thereof, wherein the proportion of the highlyunsaturated fatty acid in the constituent fatty acids of the compositionis 50 area % or more and wherein the concentration of 3-MCPD as foundupon analyzing the composition by American Oil Chemists' Societyofficial method Cd 29b-13 assay A is less than 1.80 ppm.[2] The composition according to [1], wherein the proportion of thehighly unsaturated fatty acid in the constituent fatty acids of thecomposition is 70 area % or more.[3] The composition according to [1] or [2], wherein the concentrationof 3-MCPD as found upon analyzing the composition by American OilChemists' Society official method Cd 29b-13 assay A is less than adetection limit.[4] The composition according to any one of [1] to [3], wherein thehighly unsaturated fatty acid is eicosapentaenoic acid, docosahexaenoicacid, dihomo-γ-linolenic acid, arachidonic acid, or a combinationthereof.[5] The composition according to any one of [1] to [4], which is adistillation product.[6] The composition according to any one of [1] to [5], wherein a rawmaterial of the composition is a fish oil, a microorganism oil, avegetable oil or a marine animal oil.[7] A distillation feed composition containing a highly unsaturatedfatty acid alkyl ester,

wherein the highly unsaturated fatty acid alkyl ester comprises a highlyunsaturated fatty acid alkyl ester to be enriched and

wherein the concentration of monoacyl glycerol comprising as constituentfatty acid a fatty acid having 5 or more carbon atoms fewer than thehighly unsaturated fatty acid which constitutes the highly unsaturatedfatty acid alkyl ester to be enriched is less than 10,000 ppm and/or theiron concentration is less than 0.20 ppm.

[8] The composition according to [7], wherein the concentration ofmonoacyl glycerol comprising as the constituent fatty acid a fatty acidhaving 6 carbon atoms fewer than the highly unsaturated fatty acid whichconstitutes the highly unsaturated fatty acid alkyl ester to be enrichedis less than 10,000 ppm.[9] The composition according to [7] or [8], wherein the chlorineconcentration is less than 10 ppm.[10] The composition according to any one of [7] to [9], wherein thehighly unsaturated fatty acid alkyl ester to be enriched is an alkylester of eicosapentaenoic acid, docosahexaenoic acid, dihomo-γ-linolenicacid, or arachidonic acid, or a combination thereof.[11] The composition according to any one of [7] to [10], wherein a rawmaterial of the composition is a fish oil, a microorganism oil, avegetable oil or a marine animal oil.[12] A method for producing a composition containing a highlyunsaturated fatty acid or an alkyl ester thereof, which comprises:(1) alkyl esterifying a raw material containing a triglyceridecomprising a highly unsaturated fatty acid as constituent fatty acid toprepare a composition containing a highly unsaturated fatty acid alkylester;(2) at least one selected from among (a) reducing to less than 10,000ppm the concentration of a monoacyl glycerol that comprises asconstituent fatty acid a fatty acid that has 5 or more carbon atomsfewer than the highly unsaturated fatty acid that constitutes the highlyunsaturated fatty acid alkyl ester to be enriched in the compositionprepared in step (1), (b) reducing the iron concentration in thecomposition prepared in step (1) to less than 0.20 ppm, and (c) reducingthe chlorine concentration in the composition prepared in step (1) toless than 10 ppm; and(3) distilling the composition resulting from step (2) and collectingthe main distillate fraction.[13] The method according to [12], wherein the concentration of 3-MCPDas found upon analyzing the main distillate fraction from step (3) byAmerican Oil Chemists' Society official method Cd 29b-13 assay A is lessthan 1.80 ppm.[14] The method according to [12] or [13], wherein step (2)(a) isperformed by silica gel chromatography.[15] The method according to any one of [12] to [14], whereindistillation in step (3) is rectification.[16] The method according to any one of [12] to [15], wherein theconcentration of monoacyl glycerol comprising as the constituent fattyacid a fatty acid that has 6 carbon atoms fewer than the highlyunsaturated fatty acid that constitutes the highly unsaturated fattyacid alkyl ester to be enriched is reduced to less than 10,000 ppm instep (2).[17] The method according to any one of [12] to [16], wherein the highlyunsaturated fatty acid is eicosapentaenoic acid, docosahexaenoic acid,dihomo-γ-linolenic acid, arachidonic acid, or a combination thereof.[18] The method according to any one of [12] to [17], wherein the rawmaterial is a fish oil, a microorganism oil, a vegetable oil or a marineanimal oil.

In one aspect, the present invention relates to the following:

[A1] A composition containing highly unsaturated fatty acid or alkylester thereof, wherein the proportion of the highly unsaturated fattyacid in the constituent fatty acids of the composition is 50 area % ormore and wherein the concentration of 3-MCPD as found upon analyzing thecomposition by American Oil Chemists' Society official method Cd 29b-13assay A is less than 1.80 ppm.[A2] The composition according to [A1], wherein the proportion of thehighly unsaturated fatty acid in the constituent fatty acids of thecomposition is 70 area % or more.[A3] The composition according to [A1] or [A2], wherein theconcentration of 3-MCPD as found upon analyzing the composition byAmerican Oil Chemists' Society official method Cd 29b-13 assay A is lessthan a detection limit.[A4] The composition according to any one of [A1] to [A3], wherein thehighly unsaturated fatty acid is eicosapentaenoic acid, docosahexaenoicacid, dihomo-γ-linolenic acid, arachidonic acid, or a combinationthereof.[A5] The composition according to any one of [A1] to [A4], which is adistillation product.[A6] The composition according to any one of [A1] to [A5], which isproduced from a raw material derived from a fish oil, a microorganismoil, a vegetable oil or a marine animal oil.[A7] A distillation feed composition containing a highly unsaturatedfatty acid alkyl ester,

wherein the highly unsaturated fatty acid alkyl ester comprises a highlyunsaturated fatty acid alkyl ester to be enriched and

wherein the concentration of monoacyl glycerol comprising as constituentfatty acid a fatty acid having 5 or more carbon atoms fewer than thehighly unsaturated fatty acid which constitutes the highly unsaturatedfatty acid alkyl ester to be enriched is less than 10,000 ppm or theiron concentration is less than 0.20 ppm.

[A8] The composition according to [A7], wherein the concentration ofmonoacyl glycerol comprising as the constituent fatty acid a fatty acidhaving 6 carbon atoms fewer than the highly unsaturated fatty acid whichconstitutes the highly unsaturated fatty acid alkyl ester to be enrichedis less than 10,000 ppm.[A9] The composition according to [A7] or [A8], wherein the chlorineconcentration is less than 10 ppm.[A10] The composition according to any one of [A7] to [A9], wherein thehighly unsaturated fatty acid alkyl ester to be enriched is an alkylester of eicosapentaenoic acid, docosahexaenoic acid, dihomo-γ-linolenicacid, or arachidonic acid, or a combination thereof.[A11] The composition according to any one of [A7] to [A10], wherein araw material of the composition is derived from a fish oil, amicroorganism oil, a vegetable oil or a marine animal oil.[A12] A method for producing a composition containing a highlyunsaturated fatty acid or an alkyl ester thereof, which comprises:(1) alkyl esterifying a raw material containing a triglyceridecomprising a highly unsaturated fatty acid as constituent fatty acid toprepare a composition containing a highly unsaturated fatty acid alkylester;(2) at least one selected from among (a) reducing to less than 10,000ppm the concentration of a monoacyl glycerol that comprises asconstituent fatty acid a fatty acid that has 5 or more carbon atomsfewer than the highly unsaturated fatty acid that constitutes the highlyunsaturated fatty acid alkyl ester to be enriched in the compositionprepared in step (1), (b) reducing the iron concentration in thecomposition prepared in step (1) to less than 0.20 ppm, and (c) reducingthe chlorine concentration in the composition prepared in step (1) toless than 10 ppm; and(3) distilling the composition resulting from step (2) and collectingthe main distillate fraction.[A13] The method according to [A12], wherein the concentration of 3-MCPDas found upon analyzing the main distillate fraction from step (3) byAmerican Oil Chemists' Society official method Cd 29b-13 assay A is lessthan 1.80 ppm.[A14] The method according to [A12] or [A13], wherein step (2)(a) isperformed by silica gel chromatography.[A15] The method according to any one of [A12] to [A14], whereindistillation in step (3) is rectification.[A16] The method according to any one of [A12] to [A15], wherein theconcentration of monoacyl glycerol comprising as the constituent fattyacid a fatty acid that has 6 carbon atoms fewer than the highlyunsaturated fatty acid that constitutes the highly unsaturated fattyacid alkyl ester to be enriched is reduced to less than 10,000 ppm instep (2).[A17] The method according to any one of [A12] to [A16], wherein thehighly unsaturated fatty acid is eicosapentaenoic acid, docosahexaenoicacid, dihomo-γ-linolenic acid, arachidonic acid, or a combinationthereof.[A18] The method according to any one of [A12] to [A17], wherein the rawmaterial is derived from a fish oil, a microorganism oil, a vegetableoil or a marine animal oil.

Advantageous Effects of Invention

According to the present invention, compositions comprising highconcentrations of PUFA or PUFA alkyl esters while containing fatty acidesters of 3-MCPD at low concentrations can be produced in a consistentmanner.

DESCRIPTION OF EMBODIMENTS

On the following pages, the present invention are described in detail.Hereinafter, fatty acids are sometimes designated using numericalexpressions in which the number of carbon atoms, the number of doublebonds and the positions of double bonds are indicated in a simplifiedway by combining numbers and letters in the alphabet. For instance, asaturated fatty acid having 20 carbon atoms may be designated as“C20:0”, a monovalent unsaturated fatty acid having 18 carbon atomsdesignated as “C18:1”, eicosapentaenoic acid designated as “C20:5 n-3”,and so on. The symbol “n-” represents the position of a double bond ascounted from the terminal methyl group in a fatty acid; for example,“n-3” indicates that the bond between the third and fourth carbon atomsas counted from the terminal methyl group in a fatty acid is a doublebond. This method of designation is well known to persons skilled in theart and fatty acids designated in accordance with this method can bereadily identified by any person skilled in the art.

As used herein, the team “highly unsaturated fatty acids” means fattyacids having 18 or more carbon atoms and 3 or more double bonds. Highlyunsaturated fatty acids can, for example, be fatty acids having 20 ormore carbon atoms and 3 or more or even 4 or more double bonds, or fattyacids having 20 or more carbon atoms and 5 or more double bonds.Exemplary highly unsaturated fatty acids include α-linolenic acid (18:3n-3), γ-linolenic acid (18:3 n-6), dihomo-γ-linolenic acid (20:3 n-6),arachidonic acid (20:4 n-6), eicosapentaenoic acid (C20:5 n-3),docosapentaenoic acid (22:5 n-6), and docosahexaenoic acid (22:6 n-3).

As used herein, the term “crude oil” means an oil that is a mixture ofthe lipids, as extracted from organisms. As used herein, the term“refined oil” means an oil that is obtained from crude oil by performingat least one fat/oil refining step selected from the group consisting ofa degumming step, a deacidifying step, a decoloring step and adeodorizing step so that off-target substances such as phospholipids andsterols will be removed from the crude oil. A person skilled in the artcan distinguish a crude oil from a refined oil by routine analysis.

As used herein, a composition containing highly unsaturated fatty acidsor alkyl esters thereof means either a fatty acid composition containinghighly unsaturated fatty acids or a fatty acid alkyl ester compositioncontaining alkyl esters of highly unsaturated fatty acids. Here, thefatty acid composition is a composition containing fatty acids as majorconstituents, and the fatty acid alkyl ester composition is acomposition containing alkyl esters of fatty acids as majorconstituents.

As used herein, collective terms (such as highly unsaturated fattyacids, alkyl esters of highly unsaturated fatty acids, etc.) do notexclude the possibility for the presence of multiple constituents unlessthe context clearly indicates to the contrary. Hence, collective termsusually mean the presence of at least one constituent.

<Compositions Containing Highly Unsaturated Fatty Acids or Alkyl EstersThereof, with Reduced Concentrations of Fatty Acid Esters of 3-MCPD>

The present invention provides a composition containing highlyunsaturated fatty acids or alkyl esters thereof, wherein the proportionof highly unsaturated fatty acids in the constituent fatty acids of thecomposition is 50 area % or more and wherein the concentration of 3-MCPDas found upon analyzing the composition by American Oil Chemists'Society official method Cd 29b-13 assay A is less than 1.80 ppm(hereinafter, the composition is sometimes referred to as thecomposition of the present invention.)

In the present invention, the highly unsaturated fatty acid is notparticularly limited if alkyl esters thereof are obtained as a maindistillate upon enrichment by distillation. The highly unsaturated fattyacid may be eicosapentaenoic acid, docosahexaenoic acid,dihomo-γ-linolenic acid, arachidonic acid, or combinations thereof. Inpreferred embodiments, the highly unsaturated fatty acid can beeicosapentaenoic acid, docosahexaenoic acid, or a combination thereof.In more preferred embodiments, the highly unsaturated fatty acid can beeicosapentaenoic acid.

The proportion of highly unsaturated fatty acids in the constituentfatty acids of the composition of the present invention can be 50 area %or more, for example, 55 area % or more, 60 area % or more, 65 area % ormore, 70 area % or more, 75 area % or more, 80 area % or more, 85 area %or more, 90 area % or more, 95 area % or more, or 96 area % or more. Onthe other hand, in one embodiment, the proportion of highly unsaturatedfatty acids in the constituent fatty acids of the composition of thepresent invention can be 99 area % or less, for example, 98 area % orless, 95 area % or less, 90 area % or less, 85 area % or less, 80 area %or less, 75 area % or less, 70 area % or less, 65 area % or less, 60area % or less, or 55 area % or less. The proportion of highlyunsaturated fatty acids in the constituent fatty acids of thecomposition of the present invention may be e.g. from 50 to 99 area %,from 50 to 98 area %, from 50 to 95 area %, from 50 to 90 area %, from50 to 85 area %, from 50 to 80 area %, from 50 to 75 area %, from 50 to70 area %, from 50 to 65 area %, from 50 to 60 area %, from 55 to 99area %, from 55 to 98 area %, from 55 to 95 area %, from 55 to 90 area%, from 55 to 85 area %, from 55 to 80 area %, from 55 to 75 area %,from 55 to 70 area %, from 55 to 65 area %, from 55 to 60 area %, from60 to 99 area %, from 60 to 98 area %, from 60 to 95 area %, from 60 to90 area %, from 60 to 85 area %, from 60 to 80 area %, from 60 to 75area %, from 65 to 99 area %, from 65 to 98 area %, from 65 to 95 area%, from 65 to 90 area %, from 65 to 85 area %, from 65 to 80 area %,from 65 to 75 area %, from 70 to 99 area %, from 70 to 98 area %, from70 to 95 area %, from 70 to 90 area %, from 70 to 85 area %, from 70 to80 area %, from 70 to 75 area %, from 75 to 99 area %, from 75 to 98area %, from 75 to 95 area %, from 75 to 90 area %, from 75 to 85 area%, or from 75 to 80 area %.

In one aspect the highly unsaturated fatty acid can be eicosapentaenoicacid, and the proportion of highly unsaturated fatty acids in theconstituent fatty acids of the composition of the present invention canbe from 50 to 99 area %, from 50 to 98 area %, from 50 to 95 area %,from 50 to 90 area %, from 50 to 85 area %, from 50 to 80 area %, from50 to 75 area %, from 50 to 70 area %, from 50 to 65 area %, from 50 to60 area %, from 55 to 99 area %, from 55 to 98 area %, from 55 to 95area %, from 55 to 90 area %, from 55 to 85 area %, from 55 to 80 area%, from 55 to 75 area %, from 55 to 70 area %, from 55 to 65 area %, orfrom 55 to 60 area %.

In another aspect the highly unsaturated fatty acid can beeicosapentaenoic acid, and the proportion of highly unsaturated fattyacids in the constituent fatty acids of the composition of the presentinvention can be from 60 to 99 area %, from 60 to 98 area %, from 60 to95 area %, from 60 to 90 area %, from 60 to 85 area %, from 65 to 99area %, from 65 to 98 area %, from 65 to 95 area %, from 65 to 90 area%, from 65 to 85 area %, from 70 to 99 area %, from 70 to 98 area %,from 70 to 95 area %, from 70 to 90 area %, from 70 to 85 area %, from75 to 99 area %, from 75 to 98 area %, from 75 to 95 area %, from 75 to90 area %, or from 75 to 85 area %.

In yet another aspect the highly unsaturated fatty acid can beeicosapentaenoic acid, and the proportion of highly unsaturated fattyacids in the constituent fatty acids of the composition of the presentinvention can be from 60 to 80 area %, from 65 to 80 area %, from 70 to80 area %, or from 75 to 80 area %.

Having high proportions of highly unsaturated fatty acids, thecomposition of the present invention is suitable as materials for themanufacture of pharmaceuticals or supplements that contain highlyunsaturated fatty acid as an active ingredient.

As used herein, the term “area %” which represents the proportion ofhighly unsaturated fatty acids in the constituent fatty acids of acomposition may be explained as follows: the composition is analyzed byusing a gas chromatograph equipped with a hydrogen flame ionizationdetector (FID) (GC-FID); the peaks of the respective components in theobtained chart are identified and the peak areas for the respectivefatty acids are determined using Agilent ChemStation integratingalgorithm (Revision C.01.03[37], Agilent Technologies); “area %” is theproportion of an individual peak area relative to the total sum of thepeak areas for the respective fatty acids, and represents the relativecontent of the component at that peak. In the field of oil chemistry,area % is used as a unit practically synonymous with wt %. See theStandard Methods for the Analysis of Fats, Oils and Related Materialsestablished by Japan Oil Chemists' Society (JOCS), 2013 Edition,2.4.2.1-2013, Makeup of Fatty Acids (FID constant temperature gaschromatography) and Id. 2.4.2.2-2013, Makeup of Fatty Acids (FIDelevated temperature gas chromatography). Analysis conditions for gaschromatography are as set out below.

GC-FID Measurement Conditions

GC: 6890N (Agilent Technologies)

Column: DB-WAX (Agilent Technologies)

30 m×0.25 mm ID, 0.25 μm film thickness

Carrier gas: helium, 1 mL/min

Injection port: 250° C., 1 μL, Split (1:100)

Column temperature: 180° C.=>3° C./min=>230° C., retained for 15 min

Detector: FID, 250° C.

Makeup gas: nitrogen, 45 ml/min.

In embodiments where the composition of the present invention is a fattyacid composition containing highly unsaturated fatty acid, theproportion of the highly unsaturated fatty acid in the constituent fattyacids is determined by the following method. Briefly, in accordance withAOCS official method Ce 1b-89, the fatty acid composition is methylesterified and then subjected to GC under the foregoing conditions, withthe area % of the highly unsaturated fatty acids being calculated in thesame way as noted above.

In this case, the constituent fatty acids of the composition means freefatty acids in the fatty acid composition.

In embodiments where the composition of the present invention is a fattyacid alkyl ester composition containing alkyl esters of highlyunsaturated fatty acid, the proportion of the highly unsaturated fattyacid in the constituent fatty acids of the composition is determined bythe following method. Briefly, the fatty acid alkyl ester composition isanalyzed by gas chromatography under the foregoing conditions and theproportion of the peak areas for the highly unsaturated fatty acid alkylesters relative to the total sum of the peak areas for the fatty acidalkyl esters (area %) is calculated.

In this case, the constituent fatty acids of the composition means thefatty acids that constitute the fatty acid alkyl esters in the fattyacid alkyl ester composition.

The alkyl group in the highly unsaturated fatty acid alkyl esters is analkyl group that is derived from lower alcohols commonly used in alkylesterification of fatty acids, and may be exemplified by an alkyl grouphaving one carbon atom (a methyl group) or two carbon atoms (an ethylgroup). In preferred embodiments, the highly unsaturated fatty acidalkyl esters may be highly unsaturated fatty acid ethyl esters.

The composition of the present invention is such that the concentrationof 3-MCPD as found upon analyzing the composition by American OilChemists' Society official method Cd 29b-13 assay A has been reduced toless than 1.80 ppm (mg/kg), for example, less than 1.70 ppm, less than1.60 ppm, less than 1.50 ppm, less than 1.40 ppm, less than 1.30 ppm,less than 1.20 ppm, less than 1.10 ppm, less than 1.00 ppm, less than0.90 ppm, less than 0.80 ppm, less than 0.70 ppm, less than 0.60 ppm,less than 0.50 ppm, less than 0.40 ppm, less than 0.30 ppm, less than0.20 ppm, less than 0.10 ppm, less than 0.09 ppm, less than 0.08 ppm,less than 0.07 ppm, less than 0.06 ppm, less than 0.05 ppm, less than0.04 ppm, less than 0.03 ppm, less than 0.02 ppm, or less than 0.01 ppm.In some embodiments, the concentration of 3-MCPD is more than zero ppm.On the other hand, in one embodiment, the composition of the presentinvention is such that the concentration of 3-MCPD as found uponanalyzing the composition by American Oil Chemists' Society officialmethod Cd 29b-13 assay A can be 0.01 ppm or more, for example, 0.02 ppmor more. Also, the composition of the present invention may be such thatthe concentration of 3-MCPD as found upon analyzing the composition byAmerican Oil Chemists' Society official method Cd 29b-13 assay A can be0.01 ppm or more, and less than 1.80 ppm, less than 1.70 ppm, less than1.60 ppm, less than 1.50 ppm, less than 1.40 ppm, less than 1.30 ppm,less than 1.20 ppm, less than 1.10 ppm, less than 1.00 ppm, less than0.90 ppm, less than 0.80 ppm, less than 0.70 ppm, less than 0.60 ppm,less than 0.50 ppm, less than 0.40 ppm, less than 0.30 ppm, less than0.20 ppm, less than 0.10 ppm, less than 0.09 ppm, less than 0.08 ppm,less than 0.07 ppm, less than 0.06 ppm, less than 0.05 ppm, less than0.04 ppm, less than 0.03 ppm, or less than 0.02 ppm. Also, thecomposition of the present invention may be such that the concentrationof 3-MCPD as found upon analyzing the composition by American OilChemists' Society official method Cd 29b-13 assay A can be 0.02 ppm ormore, and less than 1.80 ppm, less than 1.70 ppm, less than 1.60 ppm,less than 1.50 ppm, less than 1.40 ppm, less than 1.30 ppm, less than1.20 ppm, less than 1.10 ppm, less than 1.00 ppm, less than 0.90 ppm,less than 0.80 ppm, less than 0.70 ppm, less than 0.60 ppm, less than0.50 ppm, less than 0.40 ppm, less than 0.30 ppm, less than 0.20 ppm,less than 0.10 ppm, less than 0.09 ppm, less than 0.08 ppm, less than0.07 ppm, less than 0.06 ppm, less than 0.05 ppm, less than 0.04 ppm, orless than 0.03 ppm.

As herein referred to, analysis by American Oil Chemists' Society (AOCS)official method Cd 29b-13 assay A is performed by the followingprocedure which is familiar to a skilled person.

To 100 mg of a sample, 100 μL of a standard solution of3-MCPD-d5-dipalmitate (diluted with toluene to make 5 ppm 3-MCPD-d5) and600 μL of diethyl ether are added and after mixing under stirring untilthe sample is completely dissolved, the mixture is cooled at between−22° C. and −25° C. for about 15 minutes. Subsequently, 350 μL of amethanol solution of sodium hydroxide (0.25 g of sodium hydroxide isdissolved in 100 mL of methanol) is added and the mixture is stirredthoroughly, followed by reaction at between −22° C. and −25° C. for 16hours or longer. At the same temperature, 600 μL of an acidic solutionof sodium bromide (as prepared by dissolving 600 g of sodium bromide in1 L of purified water and then adding 3 mL of 85% phosphoric acid) isadded to quench the reaction and the organic layer separated from theaqueous layer is bubbled with nitrogen until it is concentrated to avolume of about 100 μL. Subsequently, 600 μL of hexane is added andafter vigorous agitation, the mixture is allowed to settle for 5 to 10minutes undisturbed so as to remove the organic layer; this process isrepeated twice. To the remaining aqueous layer, 600 μL of a liquidmixture of diethyl ether and ethyl acetate (3:2, V/V) is added and themixture is vigorously agitated, followed by recovery of the organiclayer; this process is repeated three times. The three recovered organiclayers are combined and dehydrated with anhydrous sodium sulfate. Thedehydrated organic layer is bubbled with nitrogen until it isconcentrated to a volume of 200 μL; subsequently, 20 μL of a solution ofsaturated phenylboronic acid in diethyl ether is added and mixture isvigorously agitated for 10 seconds; the mixture is then bubbled withnitrogen to remove the solvent entirely. To the residue, 200 μL ofisooctane is added and the mixture is vigorously agitated for 10 secondsand the resulting solution is used as a sample for GC-MS.

To construct a calibration curve for quantification of 3-MCPD,3-MCPD-dipalmitate is dissolved in toluene to give 3-MCPD concentrationsof 0 ppm, 0.5 ppm, 1 ppm and 5 ppm to prepare standard solutions of3-MCPD, which are analyzed in the same manner as with the sampledescribed above.

Analysis conditions for GC-MS are as set out below.

GC-MS Conditions

GC: GC-2010 and GCMS-QP2010 (SHIMADZU)

Column: DB-5 ms (Agilent Technologies)

30 m×0.25 mm ID, 0.25 μm film thickness

Carrier gas: helium, 1.2 mL/min

Injection port: 250° C., 1 splitless, sampling time 1 min

Column temperature: 85° C., retained for 0.5 min=>6° C./min=>150° C.,retained for 5 min=>12° C./min=>180° C.=>25° C./min=>280° C., retainedfor 7 min.

Ionization temperature: 200° C.

Interface temperature: 200° C.

Ionization method: EI; SIM monitoring was conducted at the followingvalues of m/z:

-   -   3-MCPD-d5: m/z=149, 150, 201, 203    -   3-MCPD: m/z=146, 147, 196, 198

For quantification, m/z values of 150 for 3-MCPD-d5 and 147 for 3-MCPDare used, and the other values are used to verify the target substances.

In the above-described method of analysis, 3-MCPD in the sample, whetherit is a free or an ester form, is detected as 3-MCPD per se. Hence,measured values obtained in the above-described method of analysisrepresent the sum content (ppm (mg/kg)) of the free form of 3-MCPDinitially present in the sample and a free form of 3-MCPD that can beformed from the ester form of 3-MCPD.

In one aspect herein the composition of the present invention is suchthat the concentration of 3-MCPD as found upon analyzing the compositionby American Oil Chemists' Society official method Cd 29b-13 assay A canbe 0 ppm or more, and less than 1.80 ppm. In this case, the compositionof the present invention can encompass a 3-MCPD-free composition. Inother embodiments, the composition of the present invention contains3-MCPD (namely, 3-MCPD or a fatty acid ester of 3-MCPD) and theconcentration of 3-MCPD as found upon analyzing the composition byAmerican Oil Chemists' Society official method Cd 29b-13 assay A can beless than 1.80 ppm.

The composition of the present invention may be such that theconcentration of 3-MCPD as found upon analyzing the composition byAmerican Oil Chemists' Society official method Cd 29b-13 assay A is lessthan the lower limit of quantification, preferably less than a detectionlimit of the method of American Oil Chemists' Society official method Cd29b-13 assay A.

Highly unsaturated fatty acids such as eicosapentaenoic acid are knownto be abundant in certain kinds of microorganism oils, vegetable oils ormarine animal oils. Hence, these can be used as raw materials for thecomposition of the present invention. Raw materials for the compositionof the present invention may specifically be exemplified by: fish oilssuch as sardine oil, tuna oil, bonito oil, menhaden oil, cod liver oil,herring oil, capelin oil, and salmon oil; marine animal oils derivedfrom crustaceans such as krill; vegetable oils as derived from perilla,flax, soybean, and rapeseed; and oils derived from lipid-producingmicroorganisms including yeasts such as the genus Yarrowia, filamentousfungi belonging, for example, to the genus Mortierella, the genusPenicillium, the genus Aspergillus, the genus Rhodotorula, and the genusFusarium, algae such as the genus Euglena, and stramenopiles. Thecomposition of the present invention may be an oil derived fromgenetically engineered microorganisms transfected with a gene such as agenetically modified variant A9 elongase gene. Alternatively, oilsderived from genetically engineered plants, namely, oilseed plants suchas species of the genus Brassica, sunflower, corn, cotton, flax, andsafflower that have been transfected with a gene such as a variant Δ9elongase gene by gene recombinant technology can also be used as rawmaterials for the composition of the present invention. Geneticallyengineered vegetable oils, genetically engineered microorganism oils andso forth can, for example, be illustrated by those which are disclosedin WO 2012/027698, WO 2010/033753, etc. In a preferred embodiment, theraw materials for the composition of the present invention are fishoils, microorganism oils, vegetable oils or aquatic animal oils such asmarine animal oils, more preferably, fish oils.

The raw materials for the composition of the present invention containhighly unsaturated fatty acids mostly as glycerides. In fish oils, forexample, many kinds of fatty acids that have 14 to 22 carbon atoms and 0to 6 double bonds are contained as glycerides. In the presence of acatalyst or enzyme, glycerides are reacted with a lower alcohol such asethanol to alkyl esterify the fatty acids contained in the glyceridesand, thereafter, fatty acid alkyl esters other than the target highlyunsaturated fatty acids (such as EPA alkyl esters) are removed, wherebyhighly unsaturated fatty acid alkyl esters (such as EPA alkyl esters) ofhigh purity can be produced. In one embodiment, fatty acid alkyl estersother than the target highly unsaturated fatty acid alkyl esters (suchas EPA alkyl esters) can be removed by distillation. The presentinventors found that fatty acid esters of 3-MCPD derived from mono- ordi-acylglycerol having relatively high molecular weights become includedin large amounts into the residue left after obtaining the maindistillate fraction in distillation. Hence, in preferred embodiments,the composition of the present invention can be a distillate (distilledfraction).

It is known that upon heat treatments involved in distillation,thermally denatured trans-isomers are formed from the highly unsaturatedfatty acid alkyl esters (see, for example, European Journal of LipidScience and Technology, 108 (2006) 589-597, “Geometrical isomerizationof eicosapentaenoic and docosahexaenoic acid at high temperatures”;JAOCS, 66 (1989) 1822-1830, “Eicosapentaenoic acid geometrical isomerartifacts in heated fish oil esters”). Hence, in one embodiment, thecomposition of the present invention may further contain trans-isomersof the highly unsaturated fatty acid alkyl esters. The concentration oftrans-isomers in the composition of the present invention can be 2.5area % or less, for example, 2.3 area % or less, 2.0 area % or less, 1.8area % or less, 1.6 area % or less, 1.4 area % or less, 1.2 area % orless, 1.0 area % or less, 0.9 area % or less, 0.8 area % or less, 0.7area % or less, 0.6 area % or less, or 0.5 area % or less. On the otherhand, the concentration of trans-isomers in the composition of thepresent invention can be 0.01 area % or more, for example, 0.02 area %or more, 0.03 area % or more, 0.04 area % or more, or 0.05 area % ormore.

As herein referred to, the concentration of trans-isomers is a value asmeasured by GC analysis. Specifically, it is measured by the followingprocedure.

Ten milligrams of a sample is dissolved in 1 mL of hexane and subjectedto GC analysis under the following conditions.

[GC Analysis Conditions]

GC: 6890N (Agilent Technologies)

Column: DB-WAX (Agilent Technologies)

30 m×0.25 mm ID, 0.25 μm film thickness

Carrier gas: helium, 1 mL/min

Injection port: 250° C., 1 μL, Split (1:100)

Column temperature: 180° C.=>3° C./min=>230° C., retained for 15 min

Detector: FID, 250° C.

Makeup gas: nitrogen, 45 mL/min.

For example, concentration of five trans-isomers (A to E) of EPA ethylester (EPA-E) is calculated in the following way.

Given a sample from which C21 or higher saturated fatty acids ormonovalent unsaturated fatty acids have been removed by distillation,the trans-isomers of EPA ethyl ester (EPA-E) have the following relativeretention times, with the retention time for EPA-E being taken as one:0.98 to 0.99 for isomer A; 1.01 to 1.02 for isomer B; 1.02 to 1.03 forisomer C; 1.04 to 1.05 each for isomers D and E which provideoverlapping peaks. Among the peaks for the five isomers, those forisomers D and E overlap, allowing a detection of four peaks. The sum ofthe areas of those relative retention time peaks is described as thepeak area for the trans-isomers of EPA-E. The proportion of thetrans-isomers to EPA-E is determined and the concentration of theisomers in the sample is calculated from the EPA-E concentration in thesample.

Given a sample that contains C21 or higher saturated fatty acids ormonovalent unsaturated fatty acids, fractionation with a silver nitratecolumn is performed using 750 mg/6 mL of Discovery Ag-ION (Supelco) toremove the C21 or higher saturated fatty acids and monovalentunsaturated fatty acids before the foregoing analysis is conducted.

Consider, for example, the trans-isomers of dihomo-γ-linolenic acidethyl ester (DGLA-E); the sum of the areas of the following relativeretention time peaks is measured by the foregoing GC analysis and theproportion of the trans-isomers to DGLA-E is determined and theconcentration of the isomers in the sample is calculated from the DGLA-Econcentration in the sample.

Isomer A: relative retention time; 1.001 to 1.009

Isomer B: relative retention time; 1.01 to 1.03

(The retention time of DGLA is taken as one.)

The contents of the trans-isomers of other highly unsaturated fatty acidalkyl esters can also be measured by routine methods.

The composition of the present invention may be such that upon gaschromatographic measurement under the foregoing analysis conditions, theconcentration of trans-isomers of an EPA alkyl ester can be 2.5 area %or less, for example, 2.3 area % or less, 2.0 area % or less, 1.8 area %or less, 1.6 area % or less, 1.4 area % or less, 1.2 area % or less, 1.0area % or less, 0.9 area % or less, 0.8 area % or less, 0.7 area % orless, 0.6 area % or less, or 0.5 area % or less. On the other hand, thecomposition of the present invention is such that upon gaschromatographic measurement under the foregoing analysis conditions, theconcentration of trans-isomers of an EPA alkyl ester can be 0.01 area %or more, for example, 0.02 area % or more, 0.03 area % or more, 0.04area % or more, or 0.05 area % or more.

In preferred embodiments, the composition of the present invention issuch that upon gas chromatographic measurement under the foregoinganalysis conditions, the concentration of trans-isomers of EPA ethylester can be 2.5 area % or less, for example, 2.3 area % or less, 2.0area % or less, 1.8 area % or less, 1.6 area % or less, 1.4 area % orless, 1.2 area % or less, 1.0 area % or less, 0.9 area % or less, 0.8area % or less, 0.7 area % or less, 0.6 area % or less, or 0.5 area % orless. On the other hand, the composition of the present invention issuch that upon gas chromatographic measurement under the foregoinganalysis conditions, the concentration of trans-isomers of EPA ethylester can be 0.01 area % or more, for example, 0.02 area % or more, 0.03area % or more, 0.04 area % or more, or 0.05 area % or more.

The composition of the present invention may be such that upon gaschromatographic measurement under the foregoing analysis conditions, theconcentration of trans-isomers of a DGLA alkyl ester can be 2.5 area %or less, for example, 2.3 area % or less, 2.0 area % or less, 1.8 area %or less, 1.6 area % or less, 1.4 area % or less, 1.2 area % or less, 1.0area % or less, 0.9 area % or less, 0.8 area % or less, 0.7 area % orless, 0.6 area % or less, or 0.5 area % or less. On the other hand, thecomposition of the present invention is such that upon gaschromatographic measurement under the foregoing analysis conditions, theconcentration of trans-isomers of a DGLA alkyl ester can be 0.01 area %or more, for example, 0.02 area % or more, 0.03 area % or more, 0.04area % or more, or 0.05 area % or more.

In preferred embodiments, the composition of the present invention issuch that upon gas chromatographic measurement under the foregoinganalysis conditions, the concentration of trans-isomers of DGLA ethylester can be 2.5 area % or less, for example, 2.3 area % or less, 2.0area % or less, 1.8 area % or less, 1.6 area % or less, 1.4 area % orless, 1.2 area % or less, 1.0 area % or less, 0.9 area % or less, 0.8area % or less, 0.7 area % or less, 0.6 area % or less, or 0.5 area % orless. On the other hand, the composition of the present invention issuch that upon gas chromatographic measurement under the foregoinganalysis conditions, the concentration of trans-isomers of DGLA ethylester can be 0.01 area % or more, for example, 0.02 area % or more, 0.03area % or more, 0.04 area % or more, or 0.05 area % or more.

Fish oils and microorganism oils that contain highly unsaturated fattyacids also contain cholesterols in addition to triglycerides. Highlyunsaturated fatty acid enriched oils prepared from these feed oils alsocontain cholesterols (WO 2012/118173). What is more,cholesterol-containing oils are not completely freed of cholesterolseven if they are subjected to alkali esterification or urea adductformation. Hence, in certain embodiments herein, the composition of thepresent invention contains cholesterols. The content of cholesterolscan, for example, be 1.5 wt % or less, 0.3 wt % or less, or 0.2 wt % orless. In this connection, the content of cholesterols can, for example,be 0.01 wt % or more, or 0.02 wt % or more.

Cholesterols are compounds having a steroid skeleton represented by themolecular formula C₂₇H₄₆O, and in natural products, cholesterols arepresent in either a free or an ester form. The ester form is an acylcholesterol having a fatty acid bound to the moiety of a hydroxyl group(OH group). In the context of the present invention, the cholesterolcontent means the sum of the contents of cholesterols in a free form andan ester form. The cholesterol content is measured by the followingmethod.

To about 0.1 g of a sample, 1 mL of 0.1 g/L 5α-cholestane is added as aninternal standard and after adding 1 mL of 20 mol/L potassium hydroxidein hydrous ethanol, the mixture is heated at 100° C. for 10 minutes.After cooling, 3 mL of petroleum ether and 3 mL of saturated ammoniumsulfate are added and the mixture is stirred and allowed to settleundisturbed; subsequently, the upper layer is recovered and subjected toa gas chromatographic measurement under the following conditions. Todetermine the relative sensitivities for 5α-cholestane and freecholesterols, a hexane solution having each of 5α-cholestane andcholesterols dissolved in an amount of 25 mg is subjected to a gaschromatographic measurement and the total amount of cholesterols iscalculated.

Gas Chromatographic Analysis Conditions

Apparatus model: Agilent 6890 GC system (Agilent)

Column: DB-1 J&W 123-1012

Column temperature: 270° C.

Injection temperature: 300° C.

Injection method: Split

Split ratio: 50:1

Detector temperature: 300° C.

Detector: FID

Carrier gas: helium (39.3 kPa, constant pressure)

In one embodiment, the composition of the present invention can containas an impurity saturated fatty acids with a carbon number of not morethan 18 or alkyl esters thereof. In this case, the proportion ofsaturated fatty acids with a carbon number of not more than 18 in theconstituent fatty acids of the composition of the present invention canbe 0.1 area % or more, for example, 0.2 area % or more or 0.3 area % ormore, and less than 10 area %, for example, less than 5 area %, lessthan 4 area %, or less than 3 area %.

Highly unsaturated fatty acids can be obtained by hydrolyzing the highlyunsaturated fatty acid alkyl esters produced by the above-describedmethod.

The composition of the present invention is one that contains fattyacids or fatty acid alkyl esters as a major component and typically itcontains 50% by weight or more, 55% by weight or more, 60% by weight ormore, 65% by weight or more, 70% by weight or more, 75% by weight ormore, 80% by weight or more, 85% by weight or more, 90% by weight ormore, 95% by weight or more, 96% by weight or more, 97% by weight ormore, 98% by weight or more, 99% by weight or more, 99.5% by weight ormore, or 99.9% by weight or more of fatty acids or fatty acid alkylesters. The content of the fatty acids or fatty acid alkyl esters in thecomposition of the present invention can be confirmed by a publiclyknown technique, such as TLC/FID.

<Method for Producing a Composition Containing a Highly UnsaturatedFatty Acid or an Alkyl Ester Thereof>

The present invention provides a method for producing theabove-described composition of the present invention. The methodcomprises:

(1) alkyl esterifying a raw material containing a triglyceridecomprising a highly unsaturated fatty acid as constituent fatty acid toprepare a composition containing a highly unsaturated fatty acid alkylester;

(2) at least one selected from among (a) reducing to less than 10,000ppm the concentration of monoacyl glycerol that comprises as constituentfatty acid a fatty acid which has 5 or more carbon atoms fewer than thehighly unsaturated fatty acid that constitutes the highly unsaturatedfatty acid alkyl ester to be enriched in the composition prepared instep (1), (b) reducing the iron concentration in the compositionprepared in step (1) to less than 0.20 ppm, and (c) reducing thechlorine concentration in the composition prepared in step (1) to lessthan 10 ppm; and(3) distilling the composition resulting from step (2) and collectingthe main distillate fraction (the method is hereinafter sometimesreferred to as the method of the present invention).

According to the method of the present invention, a composition thatcontains fatty acids or fatty acid alkyl esters as a major component andcontains 95% by weight or more, 96% by weight or more, 97% by weight ormore, 98% by weight or more, 99% by weight or more, 99.5% by weight ormore, or 99.9% by weight or more of fatty acids or fatty acid alkylesters can be produced.

Hereinafter, step (1) is sometimes referred to as an alkylesterification step, step (2)(a) is sometimes referred to as a monoacylglycerol removing step, step (2)(b) is sometimes referred to as an ironremoving step, step (2)(c) is sometimes referred to as a chlorineremoving step, and step (3) is sometimes referred to as a distillationstep.

Raw materials that can be used in the method of the present inventioninclude the oils listed for the above-described composition of thepresent invention and they may specifically be exemplified by: fish oilssuch as sardine oil, tuna oil, bonito oil, menhaden oil, cod liver oil,herring oil, capelin oil, and salmon oil; marine animal oils derivedfrom crustaceans such as krill; vegetable oils as derived from perilla,flax, soybean, and rapeseed; and oils derived from lipid-producingmicroorganisms including yeasts such as the genus Yarrowia, filamentousfungi belonging, for example, to the genus Mortierella, the genusPenicillium, the genus Aspergillus, the genus Rhodotorula, and the genusFusarium, algae such as the genus Euglena, and stramenopiles. The oilsthat can be used as raw materials for the method of the presentinvention may be an oil derived from genetically engineeredmicroorganisms transfected with a gene such as a genetically modifiedvariant A9 elongase gene. Alternatively, oils derived from geneticallyengineered plants, namely, oilseed plants such as species of the genusBrassica, sunflower, corn, cotton, flax, and safflower that have beentransfected with a gene such as a variant A9 elongase gene by generecombinant technology can also be used as raw materials for the methodof the present invention. Genetically engineered vegetable oils,genetically engineered microorganism oils and so forth can, for example,be illustrated by those which are disclosed in WO 2012/027698, WO2010/033753, etc. In preferred embodiments, the raw materials used inthe method of the present invention are fish oils, microorganism oils,vegetable oils or aquatic animal oils such as marine animal oils, morepreferably fish oils.

Crude Oil Refining Step

The feed oil to be used for alkyl esterification in step (1) may be acrude oil or a refined oil. Crude oils may be obtained by any methodfrom aquatic products such as fish or marine products, and in the caseof fish oils, they are usually harvested in the following way: fish as awhole or residues that result from fish processing such as the head,skin, backbone or viscera of fish are milled, steamed and pressed to beseparated into stick water and pressed meal. The fat and oil as obtainedtogether with the stick water are centrifuged to be separated as crudefish oil.

Refined fish oils are generally obtained from crude fish oils via arefining process in which a degumming step, a deacidifying step, adecoloring step using activated clay or activated charcoal, a waterwashing step, a deodorizing step as by steam distillation, and othersteps are performed depending on the raw material from which the crudefish oils have been prepared, to thereby remove off-target substancessuch as phospholipids and sterols. In embodiments of the presentinvention, refined fish oils can be used as the raw material.

Step (1) (Alkyl Esterification Step)

Fats or oils as the feed oil are decomposed into lower alcohol esters bymeans of alcoholysis using lower alcohols. Lower alcohols include thosewhich are commonly used in the alkyl esterification of fatty acids, forexample, lower alcohols having one or two carbon atoms. Alcoholysis is atechnique by which a fat or oil is reacted with a lower alcohol such asethanol in the presence of an added catalyst or enzyme so as to form analkyl ester from a fatty acid bound to glycerin. Catalysts that may beused include an alkali catalyst, an acid catalyst, and so forth. Enzymesthat may be used include lipase.

The alcoholysis of fatty acids has been empirically found to featurehigh reaction efficiency, and after alcoholysis, there are obtainedcompositions that mainly comprise fatty acids in the form of their alkylesters. This, however, does not totally exclude the case of comprisingfatty acids in other forms than alkyl esters.

Step (2)

Step (2) is a preliminary step before distillation and it is at leastone step selected from the following (a) to (c). Briefly, step (2) canbe any one of (a) to (c), or it may consist of (a) and (b), (a) and (c),(b) and (c), or (a), (b) and (c).

(a) Monoacyl Glycerol Removing Step

In step (2)(a), before the composition prepared in step (1) thatcontains fatty acid alkyl esters is concentrated by distillation, thecontent of monoacyl glycerols that serve as the substrate for fatty acidesters of 3-MCPD is reduced. As a result, the amount of fatty acidesters of 3-MCPD that result from heat treatments during distillation tobecome included in the main distillate fraction can be reduced.

To remove monoacyl glycerols from the composition prepared in step (1)that contains fatty acid alkyl esters, one may employ existingtechniques such as repeated treatments of alkyl esterification ortreatments with adsorbents.

Esterification is an equilibrium reaction and the residual amount ofglycerides depends on the ratio between alcohol and the by-productglycerin. If the ester fractions obtained as the result of alkylesterification are again subjected to alkyl esterification, the ratiobetween alcohol and glycerin is shifted significantly more to thealcohol side than to the glycerin side, whereby the content ofglycerides can be reduced.

Treatments with adsorbents may, for example, include silica gelchromatography, treatment with activated clay, treatment with acidicclay, treatment with activated charcoal, and treatment with silica gel.Silica gel chromatography may, for example, be performed by thefollowing procedure. In the treatment with silica gel (e.g. MicrosphereD75-60A), a composition containing fatty acid alkyl esters is applied toa column packed with silica gel so that the fatty acid alkyl esters areadsorbed on the silica gel. Subsequently, ethyl acetate/hexane (1:50) ispassed through the column, the eluate is fractionated, and fractionsconsisting of MAG- and DAG-free fatty acid alkyl esters are recovered.The solvent is removed from the recovered fractions to obtain fatty acidalkyl esters. Treatment with activated clay may, for example, be carriedout by adding activated clay in an amount of 5% relative to the oil,stirring the mixture at 120° C. for 2 hours under reduced pressure, andthen filtering the mixture. Other treatments with adsorbents can beperformed by routine methods.

The monoacyl glycerol to be removed in step (2)(a) is comprises as theconstituent fatty acid a fatty acid that has 5 or more carbon atomsfewer than the highly unsaturated fatty acid that constitutes the highlyunsaturated fatty acid alkyl ester to be enriched. Here, the highlyunsaturated fatty acid alkyl ester to be enriched refers to that highlyunsaturated fatty acid alkyl ester which is intended to be enriched inthe method of the present invention. To be more specific, in thedistillation of step (3), conditions are set in such a way that thehighly unsaturated fatty acid alkyl ester to be enriched will becollected as the main distillate fraction. Hence, the highly unsaturatedfatty acid alkyl ester to be enriched is the highly unsaturated fattyacid alkyl ester that is collected as the main distillate fraction, andenriched therein, in the distillation of step (3).

In the case where two or more highly unsaturated fatty acid alkyl estersare to be enriched (for example, combinations of alkyl esters of two ormore highly unsaturated fatty acids selected from among eicosapentaenoicacid, docosahexaenoic acid, dihomo-γ-linolenic acid, and arachidonicacid are to be enriched), the concentrations of monoacyl glycerols whichcomprise as the constituent fatty acids those fatty acids which have 5or more carbon atoms fewer than the highly unsaturated fatty acid thathas the highest carbon number are reduced.

While the constituent fatty acid of monoacyl glycerol to be removed instep (2)(a) may be either saturated or unsaturated fatty acid, removalof monoacyl glycerol of saturated fatty acid is preferred.

In step (2)(a), the concentration of monoacyl glycerol which comprisesas the constituent fatty acid a fatty acid which has 5 or more carbonatoms fewer than the highly unsaturated fatty acid that constitutes thehighly unsaturated fatty acid alkyl ester to be enriched is reduced toless than 10,000 ppm, less than 9,000 ppm, less than 8,000 ppm, lessthan 7,000 ppm, less than 6,000 ppm, less than 5,000 ppm, less than4,000 ppm, less than 3,000 ppm, less than 2,000 ppm, less than 1,000ppm, less than 900 ppm, less than 800 ppm, less than 700 ppm, less than600 ppm, or less than 500 ppm. In some embodiments, the concentration ofmonoacyl glycerol is greater than zero ppm. In some embodiments, beforesaid reduction, the concentration of said monoacyl glycerol is 10,000ppm or more or the other mentioned upper limit or higher. For example,in the case where the highly unsaturated alkyl ester to be enriched isan alkyl ester of eicosapentaenoic acid (20:5 n-3), dihomo-γ-linolenicacid (20:3 n-6), or arachidonic acid (20:4 n-6) or combinations thereof,the concentration of monoacyl glycerols comprising as the constituentfatty acid a fatty acid having no more than 15 carbon atoms, preferablya fatty acid having 14 carbon atoms, is reduced to any one of the valueslisted above. If the highly unsaturated alkyl ester to be enriched is analkyl ester of docosahexaenoic acid (22:6 n-3), the concentration ofmonoacyl glycerols comprising as the constituent fatty acid a fatty acidhaving no more than 17 carbon atoms, preferably a fatty acid having 16carbon atoms, is reduced to any one of the values listed above. And, ifthe highly unsaturated alkyl ester to be enriched is a combination of analkyl ester of docosahexaenoic acid (22:6 n-3) with at least one memberselected from among alkyl esters of eicosapentaenoic acid (20:5 n-3),dihomo-γ-linolenic acid (20:3 n-6) and arachidonic acid (20:4 n-6), theconcentration of monoacyl glycerols comprising as the constituent fattyacid a fatty acid having no more than 17 carbon atoms, preferably afatty acid having 14 carbon atoms and a fatty acid having 16 carbonatoms, is reduced to any one of the values listed above.

In the distillation of step (3) a fatty acid ester of 3-MCPD, that canbe generated from a monoacyl glycerol which comprises as the constituentfatty acid a fatty acid that has 5 or more carbon atoms fewer than thehighly unsaturated fatty acid that constitutes the highly unsaturatedfatty acid alkyl ester to be enriched, can be contained in the maindistillate fraction together with said highly unsaturated fatty acidalkyl ester. Hence, if, in the case where the highly unsaturated fattyacid alkyl ester to be enriched in the distillation of step (3) is to beobtained as the main distillate, the concentration of monoacyl glycerolwhich comprises as the constituent fatty acid a fatty acid that has 5 ormore carbon atoms fewer than the highly unsaturated fatty acid thatconstitutes the highly unsaturated fatty acid alkyl ester to be enrichedis preliminarily reduced, one can obtain a composition containing ahighly unsaturated fatty acid alkyl ester having a reduced concentrationof a fatty acid ester of 3-MCPD.

The monoacyl glycerols to be removed in step (2)(a) may be those whichcomprise as the constituent fatty acids those fatty acids which have 5to 10, 5 to 9, 5 to 8, 5 to 7, 5 to 6, or 6 carbon atoms fewer than thehighly unsaturated fatty acid that constitutes the highly unsaturatedfatty acid alkyl ester to be enriched. In step (2)(a), the concentrationof these classes of monoacyl glycerols collectively may be reduced toone of the values listed above.

In some preferred embodiments, the highly unsaturated fatty acid alkylester to be enriched is eicosapentaenoic acid (20:5 n-3) alkyl ester,dihomo-γ-linolenic acid (20:3 n-6) alkyl ester, or arachidonic acid(20:4 n-6) alkyl ester, or combinations thereof, and the monoacylglycerol to be removed in step (2)(a) can be glycerol monomyristate.

In some preferred embodiments, the highly unsaturated fatty acid alkylester to be enriched is a docosahexaenoic acid (22:6 n-3) alkyl ester,and the monoacyl glycerol to be removed in step (2)(a) can be glycerolmonopalmitate.

In some preferred embodiments, the highly unsaturated fatty acid alkylester to be enriched is a combination of docosahexaenoic acid (22:6 n-3)alkyl ester with at least one member selected from amongeicosapentaenoic acid (20:5 n-3) alkyl ester, dihomo-γ-linolenic acid(20:3 n-6) alkyl ester, and arachidonic acid (20:4 n-6) alkyl ester, andthe monoacyl glycerols to be removed in step (2)(a) can consist ofglycerol monomyristate and glycerol monopalmitate.

As herein referred to, the concentrations of monoacyl glycerol (MAG) anddiacyl glycerol (DAG) in the composition are values (ppm (mg/kg)) ascalculated from the values of measurement by the following method.

A hundred microliters of the composition is sampled, accurately weighed,and dissolved in 400 μL of hexane to prepare 150 μL of a solution, whichis then subjected to thin-layer chromatography (TLC) under the followingconditions to thereby separate MAG and DAG. All bands of MAG and DAG soidentified at UV 254 nm are scraped off and after adding 1 mL of 1 Nsodium methoxide in methanol, the mixture is heated for 5 minutes underthorough stirring. Subsequently, the mixture is cooled to roomtemperature and after adding 1 mL of 1 N HCl, the mixture is stirredthoroughly. After adding 1 mL of 0.1 mg/mL C23:0 FAME (tricosanoic acidmethyl ester) in hexane and 5 mL of saturated brine, the mixture isstirred thoroughly. Using the resulting hexane layer as a sample, GC-FIDanalysis is performed under the following conditions and theconcentrations of respective fatty acids are calculated by the followingformula:

Concentration of a fatty acid [mg/kg]=(peak area for the fatty acid/peakarea for C23:0)×(10⁵/the amount [mg] of the sample subjected to TLC)

TLC Conditions

TLC plate: PLC Silica gel 60F₂₅₄ 0.5 mm, 10 cm×10 cm

Developing solvents: hexane/diethyl ether/acetic acid (7:3:0.1,vol/vol/vol)

GC-FID measurement conditions

GC: 6890N (Agilent Technologies)

Column: DB-WAX (Agilent Technologies)

30 m×0.25 mm ID, 0.25 μm film thickness

Carrier gas: helium, 1 mL/min

Injection port: 250° C., 1 μL, Split (1:100)

Column temperature: 180° C.=>3° C./min=>230° C., retained for 15 min

Detector: FID, 250° C.

Makeup gas: nitrogen, 45 mL/min.

(b) Iron Removing Step

In step (2)(b), the iron concentration is reduced to less than 0.20 ppm,less than 0.10 ppm, less than 0.09 ppm, less than 0.08 ppm, less than0.07 ppm, less than 0.06 ppm, or less than 0.05 ppm. In someembodiments, the concentration of iron is greater than zero ppm. In someembodiments, before said reduction, the concentration of iron is 0.20ppm or more or the other mentioned upper limit or higher. By reducingthe iron concentration, the formation of fatty acid esters of 3-MCPD canbe suppressed.

As herein referred to, the iron concentration (or iron content) is avalue (ppm (mg/kg)) that is calculated from measurements by ICP-MS.Specifically, it is calculated by the following procedure.

After precisely weighing 1 g of a test composition, add butyl acetate(of a grade for atomic absorption analysis; manufactured by Wako PureChemical Industries, Ltd.) to make 10 mL; the resulting solution is usedas a sample fluid.

As a standard sample, Conostan S-21 (10 ppm (Wt.)) is used. Thisstandard sample is diluted with butyl acetate to prepare samples for theconstruction of a calibration curve (0 μg/L, 0.1 μg/L, 0.5 μg/L, 1 μg/L,5 μg/L, 10 μg/L, 50 μg/L, and 100 μg/L).

The sample fluid and the samples for calibration curve are subjected toICP-MS analysis under the following conditions; a calibration curve isconstructed by automatic calculations with the software which is anaccessory to the apparatus and the iron content in the sample fluid isdetermined.

Instrument: Agilent 7700 series ICP-MS (Agilent Technologies)

RF power: 1550 W

Sampling position: 10 mm

Carrier gas: 0.45 L/min

Option gas: 20%

Makeup gas: 0.20 L/min

Spray chamber temperature: −5° C.

Sample introduction: suction under negative pressure

Measuring mode: He mode

He cell gas flow rate: 4.3 mL/min

Element to be measured: ⁵⁶Fe

Given the thus determined iron content in the sample fluid, the ironcontent in the sample composition is calculated by the followingformula:Iron content [ppm] in the sample composition=C/(W×100)

C: the iron content (μg/L) in the sample fluid as measured by ICP-MS

W: the amount of the sample composition collected (g)

The iron concentration may be reduced to less than 0.20 ppm, less than0.10 ppm, less than 0.09 ppm, less than 0.08 ppm, less than 0.07 ppm,less than 0.06 ppm, or less than 0.05 ppm by a step different from themonoacyl glycerol removing step. In some embodiments, the concentrationof iron is greater than zero ppm. Techniques for reducing the ironconcentration may be those which can be employed in the above-descriedmonoacyl glycerol removing step; other examples include acid cleaningand ion exchange. These removal techniques can be performed by routinemethods.

(c) Chlorine Removing Step

In step (2)(c), the chlorine concentration is reduced to less than 10ppm, for example, less than 9 ppm, less than 8 ppm, or less than 7 ppm.In some embodiments, the concentration of chlorine is greater than zeroppm. In some embodiments, before said reduction, the concentration ofchlorine is 10 ppm or more or the other mentioned upper limit or higher.By reducing the chlorine concentration, the formation of fatty acidesters of 3-MCPD can be suppressed.

As herein referred to, the chlorine concentration (or chlorine content)is a value (ppm (mg/kg)) as calculated from measurements by ICP-MS.Specifically, it is calculated by the following procedure.

After precisely weighing 1 g of a test composition, add butyl acetate(of a grade for atomic absorption analysis; manufactured by Wako PureChemical Industries, Ltd.) to make 10 mL; the resulting solution is usedas a sample fluid.

As a standard sample, Conostan Cl Std. (1000 ppm (Wt.)) is used. Thisstandard sample is diluted with butyl acetate to prepare samples for theconstruction of a calibration curve (0 μg/L, 0.1 μg/L, 0.5 μg/L, 1 μg/L,5 μg/L, 10 μg/L, 50 μg/L, and 100 μg/L).

The sample fluid and the samples for calibration curve are subjected toICP-MS analysis under the following conditions; a calibration curve isconstructed by automatic calculations with the software which is anaccessory to the apparatus, and the chlorine content in the sample fluidis determined.

Instrument: Agilent 7700 series ICP-MS (Agilent Technologies)

RF power: 1550 W

Sampling position: 10 mm

Carrier gas: 0.45 L/min

Option gas: 20%

Makeup gas: 0.20 L/min

Spray chamber temperature: −5° C.

Sample introduction: suction under negative pressure

Measuring mode: He mode

He cell gas flow rate: 4.3 mL/min

Element to be measured: ³⁵C1

Given the thus determined chlorine content in the sample fluid, thechlorine content in the sample composition is calculated by thefollowing formula:Chlorine content [ppm] in the sample composition=C/(W×100)

C: the chlorine content (μg/L) in the sample fluid as measured by ICP-MS

W: the amount of the sample composition collected (g)

The chlorine concentration may be reduced to less than 10 ppm, forexample, less than 9 ppm, less than 8 ppm, or less than 7 ppm by a stepdifferent from the monoacyl glycerol removing step. In some embodiments,the concentration of chlorine is greater than zero ppm. Techniques forreducing the chlorine concentration may be those which can be employedin the above-described monoacyl glycerol removing step; other examplesinclude degumming, deacidification and other techniques that arecommonly employed in the process of refining fats and oils. Theseremoval techniques can be performed by routine methods.

Step (3) (Distillation Step)

The composition that has been reduced in the concentration of monoacylglycerols in step (2) is distilled and the main distillate fraction iscollected. By setting such conditions that the main distillate fractioncomprises the highly unsaturated fatty acid alkyl esters to be enriched,one can obtain a composition that contains the highly unsaturated fattyacid alkyl esters and in which the concentration of 3-MCPD as found uponanalyzing the composition by American Oil Chemists' Society officialmethod Cd 29b-13 assay A is less than 1.80 ppm, even if fatty acidesters of 3-MCPD result from the heat treatment during distillation.Such distillation conditions can be set as appropriate for the highlyunsaturated fatty acid alkyl esters to be enriched.

The distillation step can be performed by, for example, rectification(precision distillation), molecular distillation or short-pathdistillation. These operations can be performed by routine methods, suchas those disclosed in JP H4-128250 A, JP H5-222392 A, JP H4-41457 A, andJP H6-33088 A.

Rectification is performed under high vacuum and highly unsaturatedfatty acid alkyl esters can be obtained as the main distillate byseparating it from a more volatile initial distillate and a lessvolatile residue. The conditions for rectification may be so set thatthe highly unsaturated fatty acid alkyl esters to be enriched can beenriched as the main distillate and may be illustrated by a temperaturebetween 150° C. and 200° C., for example, between 160° C. and 200° C.,or between 170° C. and 200° C., and a pressure between 1 and 300 Pa, forexample, between 1 and 200 Pa, between 1 and 100 Pa, or between 1 and 50Pa. It is preferred to obtain the main distillate at between 170° C. and200° C. with a degree of vacuum lying between 1 and 50 Pa.

Exemplary conditions for molecular distillation or short-pathdistillation include a temperature between 80° C. and 150° C., forexample, between 80° C. and 130° C., or between 80° C. and 120° C., anda pressure of less than 10×10⁻¹ Pa, for example, less than 10×10⁻² Pa orless than 10×10⁻³ Pa.

The concentration of 3-MCPD as found upon analyzing the main distillatefraction from step (3) by American Oil Chemists' Society official methodCd 29b-13 assay A is less than 1.80 ppm, for example, less than 1.70ppm, less than 1.60 ppm, less than 1.50 ppm, less than 1.40 ppm, lessthan 1.30 ppm, less than 1.20 ppm, less than 1.10 ppm, less than 1.00ppm, less than 0.90 ppm, less than 0.80 ppm, less than 0.70 ppm, lessthan 0.60 ppm, less than 0.50 ppm, less than 0.40 ppm, less than 0.30ppm, less than 0.20 ppm, less than 0.10 ppm, less than 0.09 ppm, lessthan 0.08 ppm, less than 0.07 ppm, less than 0.06 ppm, less than 0.05ppm, less than 0.04 ppm, less than 0.03 ppm, less than 0.02 ppm, or lessthan 0.01 ppm. In some embodiments, the concentration of 3-MCPD isgreater than zero ppm. In particular the concentration of 3-MCPD asfound upon analyzing the main distillate fraction from step (3) byAmerican Oil Chemists' Society official method Cd 29b-13 assay A may be0.01 ppm or more, for example, 0.02 ppm or more. What is more, theconcentration of 3-MCPD as found upon analyzing the main distillatefraction from step (3) by American Oil Chemists' Society official methodCd 29b-13 assay A may be 0.01 ppm or more, and less than 1.80 ppm, lessthan 1.70 ppm, less than 1.60 ppm, less than 1.50 ppm, less than 1.40ppm, less than 1.30 ppm, less than 1.20 ppm, less than 1.10 ppm, lessthan 1.00 ppm, less than 0.90 ppm, less than 0.80 ppm, less than 0.70ppm, less than 0.60 ppm, less than 0.50 ppm, less than 0.40 ppm, lessthan 0.30 ppm, less than 0.20 ppm, less than 0.10 ppm, less than 0.09ppm, less than 0.08 ppm, less than 0.07 ppm, less than 0.06 ppm, lessthan 0.05 ppm, less than 0.04 ppm, less than 0.03 ppm, less than 0.02ppm. The concentration of 3-MCPD as found upon analyzing the maindistillate fraction from step (3) by American Oil Chemists' Societyofficial method Cd 29b-13 assay A may be 0.02 ppm or more, and less than1.80 ppm, less than 1.70 ppm, less than 1.60 ppm, less than 1.50 ppm,less than 1.40 ppm, less than 1.30 ppm, less than 1.20 ppm, less than1.10 ppm, less than 1.00 ppm, less than 0.90 ppm, less than 0.80 ppm,less than 0.70 ppm, less than 0.60 ppm, less than 0.50 ppm, less than0.40 ppm, less than 0.30 ppm, less than 0.20 ppm, less than 0.10 ppm,less than 0.09 ppm, less than 0.08 ppm, less than 0.07 ppm, less than0.06 ppm, less than 0.05 ppm, less than 0.04 ppm, or less than 0.03 ppm.

Chromatographic Step

The method of the present invention may further comprise a refining stepafter step (3) that is based on chromatography such as high-performanceliquid column chromatography (HPLC).

The chromatographic step based on HPLC or otherwise, which is subsequentto the distillation step, is such that the contents of off-targetcomponents in the composition that results from the distillation stepare reduced by, for example, removing the off-target components,whereupon the highly unsaturated fatty acid alkyl ester is furtherenriched in the post-distillation composition. The chromatographic stepcan be performed in accordance with conventionally known methods, forexample, the method disclosed in JP H5-222392 A. Chromatography for usein the enrichment process may be exemplified by reversed-phase columnchromatography. Examples of the stationary phase (adsorbent) includepolymer beads, preferably polystyrene reticulated with DVB(divinylbenzene), and silica gel, preferably reversed-phase bound silicagel comprising C8 or C18 alkane, and C18 bound reversed-phase silica gelis particularly preferred. The adsorbent to be used in chromatographythat follows distillation in the present invention is preferablynon-polar. Any adsorbents for reversed-phase partition may be usedwithout particular limitations and an example is an octadecylsilyl (ODS)silica gel that may be used to make an ODS column.

The size of the columns to be used in the apparatus is not particularlylimited, except that it depends on the amount of the sample to bepurified. Any skilled artisan can easily determine the column ofappropriate size to be used. The diameter of each column is typicallybetween 10 and 800 mm, preferably between 50 and 800 mm, more preferablybetween 300 and 800 mm, and most preferably between 600 and 800 mm. Thelength of each column is typically between 10 and 200 mm, preferablybetween 25 and 150 mm.

The temperature of the mobile phase and column is not particularlylimited, except that it depends on the degree by which the material tobe separated will dissolve in the mobile phase. Any skilled artisan caneasily determine the temperature of the appropriate mobile phase andcolumn to be used. The column temperature is typically between 0° C. and70° C., preferably between 20° C. and 40° C.

The solvent to be used in the mobile phase may, for example, beexemplified by short-chain alcohols. Short-chain alcohols typically have1 to 6 carbon atoms. Examples of suitable short-chain alcohols includemethanol, ethanol, n-propanol, propanol, n-butanol, i-butanol, s-butanoland t-butanol. The solvent to be used in the mobile phase is preferablymethanol or ethanol, more preferably methanol. To shorten the elutiontime, it is preferred that no water is intentionally added to theshort-chain alcohols.

<Distillation Feed Composition>

The present invention also provides a distillation feed composition forobtaining the above-described composition of the present invention, andthe use of such a distillation feed composition as distillation feed ina method for producing the above-described composition of the presentinvention. The distillation feed composition contains a highlyunsaturated fatty acid alkyl ester and is reduced in the content ofmonoacyl glycerol or reduced in the iron concentration. The highlyunsaturated fatty acid alkyl ester comprises a highly unsaturated fattyacid alkyl ester to be enriched. By distilling the distillation feedcomposition to obtain a highly unsaturated fatty acid alkyl ester in adistilled fraction, it is possible to enrich the highly unsaturatedfatty acid alkyl ester while reducing the content of a fatty acid esterof 3-MCPD.

To produce the distillation feed composition of the present invention,oils that have been listed as raw materials for the composition of thepresent invention may be alkyl esterified while reducing the content ofmonoacyl glycerol or reducing the iron concentration. In one embodiment,the distillation feed composition of the present invention is producedfrom or obtainable from a raw material such as a fish oil, amicroorganism oil, a vegetable oil or a marine animal oil, such as bythe method for producing the above-described composition of the presentinvention. In a preferred embodiment, the raw material for thedistillation feed composition of the present invention is a fish oil.Alkyl esterification and reduction in the content of monoacyl glycerolor the iron concentration can be carried out by the methods describedabove in connection with the method of the present invention. In apreferred embodiment, the highly unsaturated fatty acid alkyl estercontained in the distillation feed composition of the present inventioncan be a highly unsaturated fatty acid ethyl ester. In this connection,the highly unsaturated fatty acid alkyl ester to be enriched can be analkyl ester of eicosapentaenoic acid, docosahexaenoic acid,dihomo-γ-linolenic acid or arachidonic acid, or combinations thereof. Inpreferred embodiments, the highly unsaturated fatty acid alkyl ester tobe enriched can be an alkyl ester of eicosapentaenoic acid ordocosahexaenoic acid, or a combination thereof. In a more preferredembodiment, the highly unsaturated fatty acid alkyl ester to be enrichedcan be an eicosapentaenoic acid alkyl ester.

The distillation feed composition of the present invention is acomposition that contains a fatty acid alkyl ester as a major componentand it contains 95% by weight or more, 96% by weight or more, 97% byweight or more, 98% by weight or more, 99% by weight or more, or 99.5%by weight or more, of the fatty acid alkyl ester.

The proportion of highly unsaturated fatty acid relative to all thefatty acids in the distillation feed composition of the presentinvention is 5 area % or more, for example, 10 area % or more, 15 area %or more, or 20 area % or more. On the other hand, the proportion ofhighly unsaturated fatty acid relative to all the fatty acids in thedistillation feed composition of the present invention is less than 70area % or more, for example, less than 65 area % or more, 60 area % ormore, or 55 area % or more.

The distillation feed composition of the present invention may contain asaturated fatty acid with a carbon number of not more than 18 or analkyl ester thereof as an impurity. In this case, the proportion of thesaturated fatty acid with a carbon number of not more than 18 in theconstituent fatty acids of the distillation feed composition of thepresent invention may be 0.1 area % or more, for example, 0.2 area % ormore, 0.3 area % or more, 0.4 area % or more, or 0.5 area % or more, andless than 50 area %, for example, less than 40 area %, or less than 30area %.

In preferred embodiments, with respect to monoacyl glycerols thatcomprise as the constituent fatty acid a fatty acid that has 5 or morecarbon atoms fewer than the highly unsaturated fatty acid thatconstitutes the highly unsaturated fatty acid alkyl ester to beenriched, the concentration of such monoacyl glycerol in thedistillation feed composition of the present invention is less than10,000 ppm, less than 9,000 ppm, less than 8,000 ppm, less than 7,000ppm, less than 6,000 ppm, less than 5,000 ppm, less than 4,000 ppm, lessthan 3,000 ppm, less than 2,000 ppm, less than 1,000 ppm, less than 900ppm, less than 800 ppm, less than 700 ppm, less than 600 ppm, or lessthan 500 ppm. In some embodiments, the concentration of such monoacylglycerol is greater than zero ppm.

The class of monoacyl glycerols to which the above-described upperlimits apply may be those that comprise as the constituent fatty acid afatty acid which has 5 to 10, 5 to 9, 5 to 8, 5 to 7, 5 to 6, or 6carbon atoms fewer than the highly unsaturated fatty acid thatconstitutes the highly unsaturated fatty acid alkyl ester to beenriched.

In preferred embodiments, the highly unsaturated fatty acid alkyl esterto be enriched is eicosapentaenoic acid (20:5 n-3) alkyl ester,dihomo-γ-linolenic acid (20:3 n-6) alkyl ester, or arachidonic acid(20:4 n-6) alkyl ester, or combinations thereof, and the monoacylglycerol can be glycerol monomyristate.

In preferred embodiments, the highly unsaturated fatty acid alkyl esterto be enriched is docosahexaenoic acid (22:6 n-3) alkyl ester, and themonoacyl glycerol can be glycerol monopalmitate.

In preferred embodiments, the highly unsaturated fatty acid alkyl esterto be enriched is a combination of docosahexaenoic acid (22:6 n-3) alkylester with at least one member selected from among eicosapentaenoic acid(20:5 n-3) alkyl ester, dihomo-γ-linolenic acid (20:3 n-6) alkyl ester,and arachidonic acid (20:4 n-6) alkyl ester, and the monoacyl glycerolcan consist of glycerol monomyristate and glycerol monopalmitate.

In preferred embodiments, the iron concentration in the distillationfeed composition of the present invention is less than 0.20 ppm, lessthan 0.10 ppm, less than 0.09 ppm, less than 0.08 ppm, less than 0.07ppm, less than 0.06 ppm, or less than 0.05 ppm. In some embodiments, theconcentration of iron is greater than zero ppm.

In preferred embodiment, the chlorine concentration in the distillationfeed composition of the present invention is less than 10 ppm, forexample, less than 9 ppm, less than 8 ppm, or less than 7 ppm. In someembodiments, the concentration of chlorine is greater than zero ppm.

<Mode of Utilization>

The mode in which the composition of the present invention is utilizedis not particularly limited but it is preferably in an oral dosage form,typically, in the form of oral preparations such as granules, tablets,capsules, and liquids. Uses of the composition of the present inventioninclude, for example, foods or drinks (e.g. health foods, nutraceuticalproducts, foods for specified health use, supplements, dairy products,soft drinks, foods or drinks for companion animals, and feeds forlivestock), pharmaceuticals, and quasi-drugs; supplements andpharmaceuticals are particularly preferred. Aside from food ingredientsor food products, the composition of the present invention may be usedas components to be added to animal feeds. Hence, the composition of thepresent invention can be used as ingredients or effective components forthe foods or drinks, pharmaceuticals, and quasi-drugs mentioned above,so they can preferably be used in the manufacture of those foods ordrinks, pharmaceuticals, and quasi-drugs.

Hereinafter, Examples of the present invention are described but itshould be understood that they are by no means intended to limit thescope of the present invention.

In the following Examples, the designation of “%” means % by weightunless otherwise indicated; “ppm” means ppm by weight (i.e., mg/kg)unless otherwise indicated.

In the Examples, 3-MCPD concentration means a value of measurement byAmerican Oil Chemists' Society (AOCS) official method Cd 29b-13 assay A.In addition, 3-MCPD concentration of 0.00 ppm means that 3-MCPD was notdetected by said assay method (i.e., it was less than the value ofdetection limit).

In the Examples, iron concentration of 0.00 ppm means that iron was notdetected in the measurement by the above-described ICP-MS (i.e., it wasless than the value of detection limit).

EXAMPLES

[Test 1] Effects of Iron Content on the Formation of 3-MCPD

Sardine oil as a feed was deacidified by short-path distillation and theresulting oil was ethyl esterified in the presence of an alkalicatalyst, followed by refining on silica gel and collection of an ethylester fraction. For the refining on silica gel, an open glass columnpacked with Microsphere gel D-75-60A (AGC Si-Tech Co., Ltd.) in 5volumes of the sample was used, with hexane/ethyl acetate (50:1) beingused as an eluent.

The ethyl ester fraction (fish oil ethyl ester (EE)) was subjected tothin-layer chromatography (TLC) that confirmed no detection of DAG andMAG bands.

Measurement of the iron concentration was also conducted but no iron wasdetected in the ethyl ester fraction.

To the fish oil EE, glycerol monomyristate (Wako Pure ChemicalIndustries, Ltd.; product code 321-32412) was added in an amount of 1000ppm. What is more, an aqueous solution of iron(II) sulfate heptahydratewas added to give an iron content of 0.10 ppm (Example 2) or 1.00 ppm(Comparative Example 1); alternatively, it was not added at all (Example1). Subsequently, ethanol was added to make a uniform solution. Bysubsequent evaporation and vacuum drawing, the solvent was thoroughlyremoved.

Each test section was stirred in a nitrogen stream under heating at 210°C. on an oil bath while it was sampled over time to measure the 3-MCPDconcentration. The changes in the 3-MCPD concentration of each testsection during heating are shown in Table 1.

TABLE 1 Iron content 1.00 PPM 0.00 PPM 0.10 PPM Comparative Heating timeExample 1 Example 2 Example 1 0 hr 0.00 PPM 0.00 PPM 0.00 PPM 1 hr 0.01PPM 0.04 PPM 0.21 PPM 2 hr 0.05 PPM 0.06 PPM 0.63 PPM 4 hr 0.08 PPM 0.15PPM 0.61 PPM

In Comparative Example 1 where 1.00 ppm of iron was added, 0.61 ppm of3-MCPD formed after heating for 4 hours. In contrast, Examples 1 and 2where the iron concentration was adjusted to 0.00 ppm and 0.10 ppm,respectively, had 3-MCPD contents of 0.08 ppm and 0.15 ppm even afterheating for 4 hours; those values were considerably lower than the 0.61ppm of Comparative Example 1.

[Test 2] Effects of MAG Content on the Formation of 3-MCPD

Fish oil EE (with iron concentration adjusted to 10 ppm) was prepared asin Test 1 and it was heated in a nitrogen stream at 120° C. for an hour,either alone or with glycerol monomyristate (Wako Pure ChemicalIndustries, Ltd.; product code 321-32412) being added at concentrationsof 1 to 10%.

The 3-MCPD concentrations after heating are shown in Table 2. Even atthe relatively low temperature of 120° C. which is commonly adopted fordistilling off ethyl esters of fatty acids by molecular distillation,the 3-MCPD concentration was found to increase with increasing MAGconcentration.

TABLE 2 Amount of MAG added 3-MCPD Not added 0.00 PPM  1% 0.10 PPM  2%0.18 PPM  3% 0.23 PPM  5% 0.36 PPM 10% 0.67 PPM

[Test 3] Effects of MAG Content on the Formation of 3-MCPD in theDistillation Product of Fish Oil Ethyl Ester

Fish oil containing 20 area % of EPA was ethyl esterified in thepresence of an alkali catalyst in the usual manner to prepare fish oilethyl ester 1. Fish oil ethyl ester 1 had the following characteristicdata: the proportion of EPA in the makeup of fatty acids was 20 area %;DAG and MAG each comprising C14:0 as a constituent fatty acid werecontained at the concentrations shown in Table 3; the iron concentrationwas 0.2 ppm; and the chlorine concentration was 17 ppm.

TABLE 3 DAG and MAG contents [mg/kg] in fish oil ethyl ester 1 FAspecies DAG fraction MAG fraction C12:0 0 8 C14:0 201 501 C15:0 26 30C16:0 575 1127 C16:1n-7 215 541 C16:2(9, 12) 0 95 C16:3(5, 9, 12 29 113C16:4n-1 77 232 C18:0 137 232 C18:1n-9 282 534 C18:1n-7 94 216 C18:2n-60 62 C18:4n-3 53 161 C20:4n-6 0 73 C20: 5n-3 502 1447 C22: 5n-3 0 161C22:6n-3 288 535 Others 112 216 Total 2591 6284

Then, there were prepared fish oil ethyl ester 2 as obtained by removingMAG and DAG from fish oil ethyl ester 1, fish oil ethyl ester 3 havingglycerol monomyristate added to fish oil ethyl ester 2, and fish oilethyl ester 4 having glycerol monopalmitate added to fish oil ethylester 2.

Fish oil ethyl ester 2 was prepared by the following method.

Six hundred grams of fish oil ethyl ester 1 was mixed with 2400 mL ofhexane and the resulting liquid mixture was passed through a columnpacked with a slurry of silica gel (1200 g; Microsphere D75-60A) inhexane so that the fish oil ethyl ester was adsorbed on the silica gel.Subsequently, ethyl acetate/hexane (1:50) was passed through the columnand the eluate was fractionated, followed by recovering a fractionconsisting of the fish oil ethyl ester from which the MAG and DAG hadbeen removed. From the recovered fraction, the solvent was removed bymeans of an evaporator and vacuum drawing, whereupon an MAG/DAG freefish oil ethyl ester was obtained in an amount of 585 g. Fish oil ethylester 2 thus obtained was entirely free of MAG and DAG and had iron andchlorine concentrations of 0.05 ppm and 7 ppm, respectively.

A hundred grams of fish oil ethyl ester 2 was mixed with 0.1 g ofglycerol monomyristate and the mixture was rendered uniform by thoroughdissolving to prepare fish oil ethyl ester 3. On the other hand, 100 gof fish oil ethyl ester 2 was mixed with 0.1 g of glycerol monopalmitate(Tokyo Chemical Industry Co., Ltd.; product code: G0083) and the mixturewas rendered uniform by thorough dissolving to prepare fish oil ethylester 4.

Fish oil ethyl ester 3 or 4 was used as a sample (feed composition fordistillation) and subjected to a precision distillation processconsisting of the following first and second precision distillationsteps.

The first precision distillation step is one for removing fractions ofup to C18 ethyl esters. A vacuum jacketed fractionating tube (ϕ25 mm;Kiriyama Glass) was operated using 5 units of Sulzer Lab Packing EX (25mm×50 mm; Sulzer Chemtech Ltd.) as an internal packing. Precisiondistillation was performed for a heating period of 4.0 hours, with theliquid temperature in the column bottom (bottom temperature) being set185° C. or below, the overhead vapor temperature (overhead temperature)being set at 135° C. or below, and the pressure upstream of a vacuumpump (overhead pressure, or the degree of vacuum) being set at 30 Pa orbelow. In this first precision distillation step, fractions of up to C18ethyl esters were removed as the initial distillate to obtain an EPAenriched residue that was free of the initial distillate.

In the subsequent second precision distillation step, the residue freeof the initial distillate as obtained in the first precisiondistillation step was subjected to the following precision distillation.A vacuum jacketed fractionating tube (ϕ25 mm; Kiriyama Glass) wasoperated using 5 units of Sulzer Lab Packing EX (25 mm×50 mm; SulzerChemtech Ltd.) as an internal packing. Precision distillation wasperformed for a heating period of 3.5 hours, with the liquid temperaturein the column bottom (bottom temperature) being set at 195° C., theoverhead vapor temperature (overhead temperature) being set at 150° C.,and the pressure upstream of a vacuum pump (overhead pressure, or thedegree of vacuum) being set at 30 Pa. In this second precisiondistillation step, fractions of C22 and higher ethyl esters were removedas a residue (distillation residue) to obtain a main distillate.

Eighty grams of fish oil ethyl ester 3 as a feed had EPA enriched in thefirst precision distillation step to give 26 g of a residue free ofinitial distillate. Twenty-five grams of the obtained residue free ofinitial distillate was then fed to the second precision distillationstep where EPA was further enriched to give 11 g of a main distillate.The main distillate had EPA enriched and as Table 4 shows, theproportion of EPA in the makeup of fatty acids increased from 20.9% to73.1%. On the other hand, isomers were found to have formed due to theheating in the distillation process and the main distillate fractionwere found to contain trans-isomers of EPA ethyl ester in an amount of0.8 area % (the sum of five trans-isomers; not indicated in Table 4;hereinafter the same).

What is more, the 3-MCPD concentration was 0.00 ppm in fish oil ethylester 3 as the feed and increased after distillation to 0.01 ppm in themain distillate.

A portion (77.8 g) of fish oil ethyl ester 4 as a feed had EPA enrichedin the first precision distillation step to give 29.5 g of a residuefree of initial distillate. A portion (26.4 g) of the obtained residuefree of initial distillate was then fed to the second precisiondistillation step where EPA was further enriched to give 12.6 g of amain distillate. The main distillate had EPA enriched and as Table 4shows, the proportion of EPA in the makeup of fatty acids increased from20.9% to 77.4%. On the other hand, isomers were found to have formed dueto the heating in the distillation process and the main distillatefraction were found to contain trans-isomers of EPA ethyl ester in anamount of 1.6 area %.

What is more, the 3-MCPD concentration in the main distillate was 0.00ppm, indicating no increase from the value for fish oil ethyl ester 4 asthe feed.

TABLE 4 Sample name Fish oil ethyl ester 3 Fish oil ethyl ester 4 MainMain distillate distillate Feed fraction Feed fraction Yield 15.3% 18.1%Percent EPA 53.6% 67.1% recovery C14:0 7.5 0.0 7.5 0.0 C15:0 0.4 0.0 0.40.0 C16:0 16.5 0.1 16.5 0.0 C17:0 0.4 0.0 0.4 0.0 C18:0 3.3 2.6 3.3 0.3C20:0 0.2 0.4 0.2 0.7 C20:3 n-6 0.2 0.5 0.2 0.7 C20:5 n-3 20.9 73.1 20.977.4 C22:5 n-3 2.3 0.2 2.3 0.3 C22:6 n-3 7.3 1.1 7.3 1.9 Other fattyacids 41.1 21.9 41.1 18.8 3-MCPD [PPM] 0.00 0.01 0.00 0.00

Also investigated was the distribution of 3-MCPD in each of thefractions of fish oil ethyl esters 3 and 4. The material balance for3-MCPD contained in each of the main distillate and the residue free ofmain distillate is shown in Table 5.

TABLE 5 Fish oil ethyl ester 3 Fish oil ethyl ester 4 EPA 3-MCPD EPA3-MCPD Main distillate 75.3 28.0 80.3  0.0 Residue free of 24.7 72.019.7 100.0 main distillate

It was revealed that the 3-MCPD concentration in the main distillatewould be strongly affected by a particular MAG in the feed. Consider themain distillate that specifically comprised a fraction of EPA, or a C20fatty acid component; in fish oil ethyl ester 3 where a MAG containingC14:0, or a C14 fatty acid, as a constituent fatty acid was added, themain distillate contained 28.0% of the whole 3-MCPD but in fish oilethyl ester 4 where a MAG containing C16:0, or a C16 fatty acid, as aconstituent fatty acid was added, all the 3-MCPD was contained in theresidue free of the main distillate. This showed the following: in thecase where C20 fatty acid ethyl esters including EPA ethyl ester are tobe recovered as a main distillate, fatty acid esters of 3-MCPD formedfrom MAGs containing C14 fatty acids as constituent fatty acids willbecome included in the main distillate whereas fatty acid esters of3-MCPD formed from MAGs containing C16 fatty acids as constituent fattyacids will hardly become included in the main distillate. Thus, it maywell be concluded that when the highly unsaturated fatty acids to berefined are C20-PUFAs such as EPA, the 3-MCPD concentration in thedistillation product is strongly affected by the C14 saturated fattyacid.

It should be noted here that in each of the tests conducted, the initialdistillate was entirely free of 3-MCPD or its fatty acid esters.

INDUSTRIAL APPLICABILITY

According to the present invention, compositions comprising highconcentrations of PUFA alkyl esters while containing fatty acid estersof 3-MCPD at low concentrations can be produced in a consistent manner.

All publications, patent applications, issued patents, and otherdocuments referred to in this specification are herein incorporated byreference as if each individual publication, patent application, issuedpatent, or other document was specifically and individually indicated tobe incorporated by reference in its entirety. Definitions that arecontained in text incorporated by reference are excluded to the extentthat they contradict definitions in this disclosure.

Other embodiments are set forth in the following claims.

What is claimed is:
 1. A composition that contains fatty acids or fattyacid alkyl esters as its major component, the composition containinghighly unsaturated fatty acid or alkyl ester thereof, wherein theproportion of the highly unsaturated fatty acid in the constituent fattyacids of the composition is 50 area % or more and wherein theconcentration of 3-MCPD as found upon analyzing the composition byAmerican Oil Chemists' Society official method Cd 29b-13 assay A is 0.01ppm or more and less than 1.80 ppm.
 2. The composition according toclaim 1, wherein the proportion of the highly unsaturated fatty acid inthe constituent fatty acids of the composition is 70 area % or more. 3.The composition according to claim 1, wherein the highly unsaturatedfatty acid is eicosapentaenoic acid, docosahexaenoic acid,dihomo-γ-linolenic acid, arachidonic acid, or a combination thereof. 4.The composition according to claim 1, which is a distillation product.5. The composition according to claim 1, wherein the composition isderived from a raw material selected from a fish oil, a microorganismoil, a vegetable oil or a marine animal oil.